Electronic article surveillance (EAS) systems, have in recent years, become increasingly commonplace. Such systems are now installed in a majority of academic and public libraries and are so common in retail stores as to not even cause a second look.
One type of EAS system in which alternating magnetic fields are employed, typically utilizes panels, or lattices on both sides of an exit way, thereby defining an interrogation zone through which protected articles bearing the EAS markers must pass. Both drive coils and sense coils are generally located within each lattice. Thus, when the drive coils are appropriately energized, an alternating magnetic field is created in the zone, and the presence of a marker creates a response in the sense coils. As the drive coils are energized while marker produced signals are being sensed, it is particularly important that the respective drive and sense coils in a single lattice be nulled with respect to each other, thereby minimizing inductive coupling between the respective coils. As the null condition is affected by both ferrous objects near the lattice and by ambient electric currents, it is further important that the null condition be adjustable during installation. Also, as such systems may be installed by only partially trained personnel under severe time constraints in retail stores and the like where customer traffic and extended store hours make access to the equipment by service personnel more restricted, and yet potentially subject the equipment to physical impact, it is likewise important that the lattices be simple to install, easy to adjust and rugged enough to stay in adjustment over protracted periods. Lattices typically provided in prior magnetic EAS systems, while recognizing many of the above problems, have failed to provide lattices which both avoid the problems and do so at a commercial cost acceptable to most retail merchants. This is, at least partially, due to the fact that prior art magnetic EAS systems have been designed to use at least a pair of complementary lattices, each somewhat different from the other, so that extensive assembly was necessary upon installation at a user site.